This invention relates to feed-through devices such as feed-through filters, and more particularly, to an improved method of manufacture thereof.
Broadly, a feed-through is a device used to enable communication of some sort through a membrane such as a bulkhead, housing or wall, and comprises a tubular ferrule that is threaded, pressed or soldered into an opening of the membrane. The ferrule has a central opening which may be left open for pneumatic, liquid or gaseous communication through the membrane, or may accommodate a linear or rotary shaft for mechanical communication through the membrane, or may accommodate an optical fiber or metal wire for signal optical or electrical signal communication through the membrane.
A common usage of feed-though devices is for electrical signal transmission to or from an electronic module. In such an application, a solid wire passes through the central opening of the ferrule, and an encapsulant surrounding the wire within the central opening insulates the wire from the ferrule and provides an environmental seal between the module and the ambient medium. If a hermetic seal is required (in medical applications, for example), the space between the wire and the inside diameter of the ferrule may be filled with a glass or ceramic composition, which is then fired and bonded to the ferrule and wire by brazing; see, for example, the U.S. Pat. No. 5,650,759 to Hittman et al., issued on Jul. 22, 1997. In other applications, an epoxy or thermosetting plastic material may be used as an encapsulant. Once the ferrule is threaded, pressed or soldered into an opening in the module wall/membrane, the end of the wire disposed inside the housing is attached to a circuit supported therein, while the end of the wire outside the housing may be mated to a suitable connector, for example. In a particularly advantageous mechanization, a portion of the ferrule is enlarged to accommodate a capacitor (discoidal or tubular or chip) electrically coupled between the wire and the ferrule/housing; such devices are commonly referred to as feed-through filters, and provide high frequency filtering in addition to electrical signal communication. Inductive and/or resistive elements may also be placed in the ferrule to form various well-known filter topologies.
The manufacture of feed-through devices typically involves a significant amount of manual labor, and is therefore both costly and time-consuming. Additionally, special fixtures must be provided for maintaining concentricity of the wire within the ferrule opening prior to injection of the encapsulant. Further, the opening must be sealed at both ends of the ferrule, and it is difficult to reliably inject the encapsulant into small openings without leaving air pockets, disturbing the orientation of the wire, or smearing encapsulant on the outer periphery of the ferrule. Accordingly, what is needed is a new method of manufacturing feed-through devices that requires less manual labor and special fixturing, and that consistently produces a high quality insulative and environmental seal with less opportunity for encapsulant spillage and smearing.
The present invention is directed to an improved method of manufacture for wire feed-through devices, wherein a pre-formed tubular seal having a central axial opening for accommodating the wire insulates the wire from the ferrule and provides a tight environmental seal between the ends of the ferrule. The seal is radially compressed and then inserted, either by itself or with the wire, into the central opening of the ferrule so that the seal is maintained in compression between the wire and an inside diameter of the ferrule. In devices where one end of the ferrule opening is enlarged to accommodate one or more filter elements, the seal is positioned in the narrow portion of the ferrule opening, and additionally serves to maintain an inherent concentricity of the wire within the ferrule during installation and attachment of the filter elements, and injection of encapsulant material into the enlarged portion of the ferrule opening. The xe2x80x9cwirexe2x80x9d may be a metal wire for accommodating electrical or mechanical feed-through functions, an optical wire for accommodating optical communication functions, a hollow tube, or some other kind of wire.
The method is particularly amenable to automation, which significantly reduces the cost and time of manufacture. Additionally, the method provides a superior environmental seal between the ends of the ferrule, while eliminating prior manufacturing drawbacks associated with maintaining concentricity of the wire and injecting encapsulant into a narrow opening between the wire and the inside diameter of the ferrule.